


Investigation: Mystery Date

by Heavenly_Pearl



Category: Bishoujo Senshi Sailor Moon | Pretty Guardian Sailor Moon (Anime & Manga)
Genre: College Entrance Exams, F/M, First Dates, Humor, Interrupted Make-out Sessions, Romance, Spying, UsaMamo Spring Exchange 2020
Language: English
Status: Completed
Published: 2020-03-18
Updated: 2020-03-18
Packaged: 2021-02-28 22:42:25
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,342
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23194942
Author URL: https://archiveofourown.org/users/Heavenly_Pearl/pseuds/Heavenly_Pearl
Summary: Usagi's little brother Shingo – now a teenager – is going out on his first date with someone but won't tell her who the lucky person is. Naturally, that means Usagi and Mamoru must follow him on their own undercover date to the movies – for Shingo's protection, of course. The fact that Usagi is tired of studying for her upcoming college entrance exams has absolutely nothing to do with it at all.Not at all.
Relationships: Chiba Mamoru/Tsukino Usagi, Tomoe Hotaru/Tsukino Shingo, Tsukino Shingo & Tsukino Usagi
Comments: 9
Kudos: 39





	Investigation: Mystery Date

**Author's Note:**

  * For [Astraearose](https://archiveofourown.org/users/Astraearose/gifts).



> NOTE BEFORE READING: This story takes place post-canon, when Usagi is eighteen and about to graduate high school. Trying to make sense of Hotaru's age in the manga is close to impossible, so for the sake of this fic, let's just say she's about the same age as Shingo, who I'm thinking is about, eh, fifteen-ish? In ninth or tenth grade? Yeah, let's go with that.

Usagi was _supposed_ to be studying for her upcoming college entrance exams.

Her motives were pure. Ami had her own exams to prepare for, so asking her boyfriend over for the afternoon to help her with English vocabulary made sense. Mamoru, after all, was the second smartest person she knew – and he happened to be fluent in English!

The fact that halfway through her tutoring session, they ended up tossing her textbooks aside and making out on top of her moon-and-bunny printed comforter… Well, that wasn't her fault. How could she possibly be expected to focus on irregular verb tenses when Mamoru had the nerve to look so damn sexy in his reading glasses?

"Usako," he murmured in between fevered kisses, "we really…should…get…back to…studying…"

His hands, however, roamed up the back of her sweater in direct contradiction of what he just said, Usagi inwardly smirking. Mamoru liked to pretend he was Mr. Responsible, but even he fell prey to his raging hormones on occasion.

"No, just a little –" She gasped, Mamoru's soft lips traveling down her jaw to that certain spot on her neck that always filled her with desire. "Yes, there. Don't stop, Mamo-chan… That feels so… Oh, Mam—"

A loud knock on her bedroom door broke the mood.

Groaning, Usagi pulled away from Mamoru, sitting up and yanking her sweater back down over her stomach. Ugh, graduation couldn't come fast enough! Mamoru had promised she could move in with him as soon as she received her diploma, and Usagi was already counting down the days – only 69 more to go! – faithfully crossing out each box on her Hello Kitty calendar with a bright pink marker. Then they could make-out twenty-four/seven, without ever having to worry about somebody interrupting them ever again.

Well, except Luna. And the other senshi. And she supposed Chibi-Usa was going to exist _someday_ …

"This had better be important," Usagi said, swinging open the door.

Her little brother Shingo – who wasn't so little anymore, having grown at least a foot over the past year – stood in the hallway, his right hand outstretched. "That thousand yen I lent you last week? Time to pay up," he said, wiggling his fingers.

"But I haven't even gotten my allowance yet!"

"Don't care. I need it back, now."

Usagi rolled her eyes. "I can't give you what I don't have, Shingo. I'm totally broke." Even her New Year's stash was gone, having blown it all on manga and video games as usual.

"Ugh, you're eighteen years old already! Isn't it about time you learned how to manage your money?"

Coming up behind Usagi after he finished re-buttoning his shirt, Mamoru placed his hands on her shoulders. "What's this about money?" he asked.

"Stupid Usagi here won't pay me back the money she owes me," Shingo said.

"Can't you wait a couple more days?" Usagi asked, pressing her palms together in front of her face in supplication. "Please? I promise I'll pay you back the second Papa gives us our allowances for the month."

"No, it has to be today! I have a da—" Shingo clamped his hand over his mouth, but the damage had already been done, Usagi perking up at that piece of information.

"Oh, my god, you have a date?!"

"No!" His cheeks burned bright red, almost matching the exact shade of his T-shirt. "I mean, kinda?"

"With who?"

"None of your beeswax."

"But, Shingo!"

Before their argument could escalate any further, Mamoru stepped in between them and got out the leather wallet Usagi had given him for Christmas – one of the reasons why she was currently low on funds. "How much does Usagi owe you, Shingo-kun?"

"A thousand yen."

He pulled out a crisp thousand yen note and handed it to Shingo, smiling. "Here. Have fun on your date."

"Thanks, Mamoru-san!" Stuffing the note in his pocket, Shingo glared at Usagi. "At least you have a rich, responsible boyfriend. Maybe the next time you need to borrow money, you should ask him first instead of your poor brother."

"It was an emergency!" she protested.

"Stocking up on Pocky, KitKat bars, and canned coffee at the conbini at eleven o'clock at night does _not_ count as an emergency."

"Hey, I was studying hard. I needed the fuel!"

"Sure, whatever," Shingo said, rolling his eyes. "Anyway, I gotta go. I don't want to be late for the movie."

"Oh, what are you seeing?"

"The new Miyaza—I mean, mind your own business!" He turned around to leave. "Go back to studying or making out or whatever you two were doing," he said with a wave over his shoulder as he made his way to the stairs.

Usagi stuck out her tongue at him and closed the door. Cheeky brat! Wait until he brought his new girlfriend – or wait, could it possibly be a _boyfriend_? – home for the first time…

"You know, Shingo-kun's right," Mamoru said. "We really should get back to studying."

He sat back down at the kotatsu table in the center of the room, reaching for the stack of flash cards Ami had made for Usagi as a study guide, but rather than taking her seat beside him, Usagi smiled her most enticing smile and crawled onto his lap, arms wrapped around his neck.

"Hey, Mamo-chan…"

"No, we are not going to spy on your little brother on his date," Mamoru said, not even giving her the chance to broach the subject.

Dammit, he knew her too well.

"Oh, 'spy' is such an ugly word," Usagi said. "I prefer to call it –" she thought back to her English vocabulary list for an appropriate synonym "– 'investigate'. Yeah, investigating! You know, just in case his date happens to be a monster in disguise or something."

"But there haven't been any more attacks since Galaxia over two years ago," he pointed out. "The odds that Shingo's date is some sort of new enemy are pretty low."

A small ache burned in Usagi's chest at the mention of Galaxia's name. Watching Mamoru's starseed get taken from him right in front of her at the airport, killing him while she did nothing but freeze in shock, would forever remain one of the worst memories of her life, one that she almost wished she had never been forced to remember.

"T-That doesn't mean that a new enemy won't show up. Like Luna says, we need to keep vigilant," she said, pushing the memory back to the recesses of her mind where it belonged. "Besides, I've been dying to see the new Miyazaki movie, too."

"You need to focus on your exams, Usako. They're only a couple of weeks away."

"But it's good to take breaks every once in a while, isn't it?" Not willing to give up, Usagi curled a strand of his dark hair around her finger. "Even Ami-chan says so nowadays."

Mamoru smirked. "Didn't we just take a break?"

Well, he wasn't wrong, but still… "Oh, come on. It's been forever since we've gone on an honest-to-goodness real date. You want to see the movie, too, don't you?"

"Not espec—"

"Please? Pretty please, with a cherry on top?" she pleaded, giving him her best puppy dog eyes.

He sighed. "You're not going to be able to focus unless we do, are you?"

"Nope!" Victorious, Usagi jumped up, offering her hand to help pull Mamoru back to his feet. "I promise, I'll study extra hard tonight to make up for it."

"No, you won't," he said with an affectionate chuckle, "but you're right. It has been a while since we've gone on a date. You deserve a reward for all the hard work you've done the past couple of weeks."

Once again wrapping her arms around his neck, Usagi stood on her tiptoes and gave him a kiss. "You're the best boyfriend ever, Mamo-chan!"

* * *

By the time they purchased their tickets and got through the long line at the concession stand – where Usagi proceeded to sweet talk Mamoru into buying her enough snacks to feed a small village – the previews were already starting. Usagi looked around the darkened theater for Shingo and his date, but it was difficult to make out much of anything beyond vague shadows.

"Do you see them anywhere?" she whispered to Mamoru.

"Usako, give the kid some privacy. Let's just find a seat and watch the movie."

"Aw, but I wanna see who his date is!" Most of the movie-goers appeared to be parents with small children, so Usagi looked one more time around the theater, focusing on the shadows that appeared to be couples. "Oh, I think that's them," she said upon locating the shadow of someone with a similar hairstyle to Shingo's. "The couple in the center of the fifth row? Come on, follow me."

Taking his free hand, she led Mamoru to a pair of seats a couple of rows behind the teenage boy and his date, a girl with straight, shoulder-length hair pulled back with a headband. 

Usagi pouted. "We should have gotten here earlier! I can't see anything when it's this dark."

"You were the one who insisted on buying snacks," Mamoru reminded her. "Speaking of which…" He handed Usagi her hot dog from the stash on his lap. "Here. You can probably get a better look at her when we're leaving."

"I guess…"

She bit off the end of the hot dog, letting out a soft moan at its juicy deliciousness. Even if it did hold them up, it was worth hitting the concession stand. Imagine going to the movies and not stuffing yourself with hot dogs, popcorn, and oversized boxes of candy!

Mamoru chuckled and reached for the chocolate bar he had bought for himself just as Usagi's phone pinged with a text message.

"Oops!" She had forgotten to turn it off when they arrived. "Here, hold that a sec," she told Mamoru, handing him the hot dog once again and pulling out her phone to quickly check the message.

Her eyes widened when she saw what it said. "Shingo's going out with _who_?!"

Momentarily forgetting where she was, Usagi had said that last part in her normal voice, catching the attention of the boy and his date.

_Crap!_

Thinking quickly, she turned to kiss Mamoru, yanking him by the shirt collar just as the boy looked over his shoulder. Despite her earlier annoyance, Usagi was grateful for the darkness. Shingo – and it was definitely Shingo – didn't seem to recognize them, only muttering "Ugh, get a room," before turning back around and whispering something else in his date's ear that Usagi couldn't hear. 

"Okay, not that I'm complaining, but what was that about?" Mamoru asked once Usagi pulled away, releasing her hold on his shirt. "Did you recognize his date?"

Usagi held up her phone, allowing him to read the text message Haruka had sent her: _Hey, did you know Hotaru-chan was going on a date with your little brother?_

"Hotaru-chan? As in, Hotaru _Tomoe_?" he whispered back, as shocked by the news as she was.

"Do you know any other Hotarus?" She frowned. "I mean, I know they're in the same class this year, and they're both members of the gardening club, but… Hotaru-chan?" She glanced back at the text message. "What should I say?"

"Nothing. The movie is about to start, so you need to turn off your phone."

"I can't just ignore it, Mamo-chan. I'll be quick."

She typed out a hurried reply: _At movies. Don't worry. Keeping an eye on them._

Mamoru let out a sigh, rubbing at his temple. "Maybe we should have picked another movie…" 

"Oh, hush." After sending the text, Usagi turned off her phone and slid it back in her pocket. "Happy? Now, give me back that hot dog."

A couple of minutes later, the previews ended and the actual movie started playing on the big screen, but Usagi paid it little attention, more interested in what was happening between the couple two rows ahead of them.

She still couldn't believe Shingo's date was Hotaru, of all people. He never mentioned anything about having a crush on her! If he had, Usagi would have been more than happy to play matchmaker…which, now that she thought about it, was probably why he hadn't said anything about it to her in the first place.

Well, Shingo seemed to be doing well enough on his own, the two of them shyly bumping hands over the armrest in between them several times before eventually entwining their fingers together. Usagi had to hold back the urge to squeal, taking a long sip of her Coke instead before nudging Mamoru's elbow.

"Look, look!" she whispered. "They're holding hands – isn't that just the cutest?"

"Usako, are you even watching the movie?" he asked. "I thought you said you were dying to see it."

"But –"

Usagi sighed, grabbing a handful of popcorn from the bucket in Mamoru's lap. Maybe he had a point. She really _had_ wanted to see the movie, and she supposed Shingo deserved some privacy. She certainly wouldn't have liked it if their positions had been reversed and her little brother had spied on her first date with Mamoru.

Resolving not to pay Shingo and Hotaru any more mind, Usagi stared up the big screen, a smile crossing her lips a couple of minutes later when Mamoru reached for her own hand, his skin comfortably warm despite the chilly temperature of the theater. Even though it was too dark to tell, Usagi imagined his cheeks were probably flushed a soft pink, Mamoru not usually one for such physical displays of affection in public. She decided to take advantage, snuggling up against him and resting her head on his shoulder as they continued watching the movie.

_This is nice_ , Usagi thought, relaxing even more when Mamoru stretched his arm around her back, pulling her even closer. It really had been a long time since they went on a proper date. Even Christmas Eve – the most romantic night of the year – had been a bust, Mamoru having caught a bad cold at the worst possible time. (Her generous offer to play "Nurse" had been turned down with a "Don't worry about me; you should take the extra time to study. I don't want you to get sick, too.") With her exam preparations and Mamoru's med school classes keeping them both busy, there never seemed to be a moment to get away.

In fact, Usagi had barely even slept for the past couple of weeks, trying to cram three years' worth of vocabulary and formulas into her brain. As she attempted to pay attention to the movie, she found herself fighting back the exhaustion that was finally catching up to her, hiding her yawns from Mamoru, who was thoroughly engrossed in the story despite claiming earlier that he had little interest in seeing the movie. Usagi smiled, lifting her chin to sneak a look at his shadowy profile. It seemed like she wasn't the only one who had needed a real break from studying.

_I really should thank Shingo later…for giving us…an excuse to…_

It was no use. Her eyelids growing heavy, Usagi drifted off to sleep in the warm, protective comfort of Mamoru's arms.

* * *

Someone lightly shook her by the shoulder.

"Usako? Hey, Usako, time to wake up."

"Just five more minutes, Luna," Usagi mumbled, stubbornly refusing to open her eyes from the wonderful dream she was having. She was at the best part, when Tuxedo Kamen swooped into her bedroom and gathered her in his strong arms, professing words of –

"The movie's over. It's time to leave," Tuxedo Kamen said, again shaking her.

No, that wasn't what he usually said…

"Huh, what?" Her eyelids fluttering open, Usagi drowsily lifted her head off Mamoru's shoulder and looked around. The lights were back on, the credits scrolling down the screen as people began exiting the theater. "Wait, did I miss the entire movie?!" she asked, wiping a bit of dry drool from her chin.

"Yeah, you did," a familiar voice said, Shingo and Hotaru coming up the aisle and stopping at the end of Usagi's and Mamoru's row. They were still holding hands. "Geez, you have got to be the worst spy in the entire world, Usagi," Shingo said with a roll of his eyes. "First you blow your cover by talking too loud and forgetting to wear a disguise, then you fall asleep in the middle of the mission? Glad the fate of the world isn't in your hands. We'd be doomed!"

Beside him, Hotaru covered her mouth with her hand, stifling a giggle, and even Mamoru had to fake a sudden coughing fit to cover up his laughter. If only Shingo knew…

"Oops, so you did recognize us?" Usagi asked sheepishly, rubbing the back of her neck.

He pointed at her head. "The hairstyle kinda gave it away, Agent Bunhead."

Dammit, she knew she should have used the Disguise Pen! Too late for that idea…

"Why _were_ you spying on us, Usagi-san?" Hotaru asked.

Letting go of Hotaru's hand, Shingo crossed his arms over his chest, glaring down at Usagi. "Yeah, why were you?"

"Oh, uh, we weren't spying!" Usagi said. "We were just out on a date, right, Mamo-chan?"

"Y-Yes, that's right," Mamoru said, backing her up like the wonderful boyfriend he was. "It was only coincidence that we ran into you."

Shingo arched an eyebrow. "It was only coincidence that you two showed up at the same movie I told you I was seeing?"

"To be fair, you didn't finish saying 'Miyazaki'," Usagi pointed out. "You might have been going to see the new Miyazawa movie instead." Whoever that was.

"Usagi…"

There was no talking her way out of this situation, was there? "Okay, fine, we were spying," she confessed. "I just wanted to know who your girlfriend was! Why didn't tell me you were dating Hotaru-chan? Why all the secrecy?"

"Uh…well…"

"Are you embarrassed of me, Shingo-kun?" Hotaru asked in a small voice.

Eyes wide, Shingo immediately pivoted around to face Hotaru, placing his hands on her upper arms. "No, of course not!" he said. "I really like you, Hotaru-chan. You're super cool and really pretty! I…uh…just…" He sighed, letting go of his hold on her and bringing his arms back down to his sides. "I don't know why I didn't tell her. I guess I wanted to wait until it was official?"

Hotaru gave him a shy smile, pushing a strand of hair behind her ear. "Official?"

"Yeah…um…"

He again looked back at Usagi, none-too-subtly jerking his head in the direction of the doors at the back of the theater.

"Oh, right!" For once, Usagi got the hint, standing up and pulling Mamoru from his seat. "Come on, Mamo-chan. We should head home and get back to studying."

They headed for the exit, Usagi taking one final look over her shoulder and mouthing the words "Good luck!" to Shingo before grabbing onto Mamoru's arm and leaving them to work things out on their own.

"You know, I hope Hotaru-chan says 'yes'," Mamoru said unexpectedly after they tossed their trash into the proper bins and exited the main doors. "They do make a cute couple."

Usagi raised an eyebrow. "I thought you weren't interested in their relationship."

"Yeah, well…" He coughed into his fist, a faint blush crossing his cheeks. "You've got me invested now."

She giggled. "You're a huge romantic at heart, Mamo-chan. Just admit it," she said, wrapping her arm around his waist as they headed back to her place, mission accomplished.

* * *

"Okay, here's an easy one. What is the English word for _yume_?" Mamoru asked from his seat on the other end of the couch.

Rather than going back upstairs to Usagi's bedroom when they returned from the movie theater, he had smartly suggested that they might get a little more actual studying done if they relocated to the much less private living room. Usagi had pouted at first, but grudgingly, she had to admit that it was easier to focus on the material when there wasn't a nice, fluffy bed around to distract her with ideas of what she would much rather be doing with Mamoru instead.

"Um…'dream'?"

"That's right. Good job!"

Usagi pumped her fist, proud of herself. They had gone through almost half of Ami's deck of flash cards, and so far, she had only missed a handful of words. Maybe this whole "studying" thing really did serve a purpose after all – not that she would ever admit it.

"That's the tenth one I got right in a row," she said. "That means I get a reward."

Flipping to the next card in the deck, Mamoru cocked an eyebrow. "Oh? And when was this decided?"

"Just now." Usagi leaned forward, twirling a strand of her long hair around her finger. "And do you know what I want?"

"Usako, I thought you promised to focus on your studies."

"I am! But one little kiss won't hurt…"

"We can't. Your mother is going to be home from the store any moment now."

"Oh, come on, just one itsy, bitsy kiss?" she pleaded, inching closer. "For encouragement?"

Mamoru sighed, eyes glancing around the room to make sure they were truly alone before smiling. "Okay, one kiss," he agreed, setting the flash cards aside on the coffee table and scooting over to bridge the gap between them.

Just as their lips were about to meet, however, they heard the front door open, followed by the sound of footsteps in the entryway and Shingo's voice calling out that he was home. They immediately split apart and moved back to their respective spots on opposite sides of the couch, Mamoru shuffling through the deck of flash cards while Usagi pretended to intently read her Japanese-to-English dictionary.

"Hey, Mama, when is dinner goin—" Shingo stopped short upon entering the living room, rolling his eyes at the sight of them. "You know, you might learn more if you turned that book the right way around, Usagi."

Usagi looked down at the random page she had turned to. Indeed, in her haste, she failed to notice that the dictionary was flipped upside down. "Oh, yeah, that might be helpful," she said with a sheepish chuckle, closing the book and setting it down on the cushion beside her as there was no point in pretending any longer that she had actually been reading it. "So?"

"So…what?"

It was Usagi's turn to roll her eyes. "So, how did it go with Hotaru-chan?" she asked. "Did she agree to be your girlfriend?"

"Oh, um, yeah." He tried to play it cool, stuffing his hands in the pockets of his jeans, but Shingo couldn't quite hide the grin that tugged at his lips.

Usagi squealed, jumping up to hug her little brother around the waist. "Your first girlfriend – I'm so happy for you!" she said. "You two make such an adorable couple."

"Aw, come on, Usagi, don't make such a big fuss over everything," he said, although for once he didn't try to push her away. "It's not like we're getting married or anything…"

"Of course not, but you never know. After all, I started dating Mamo-chan when I was around your age, and we're definitely gonna be together forever! So, maybe in the future…?"

Then Hotaru would be her sister-in-law! That would be pretty cool.

Shingo chuckled, ruffling Usagi's bangs after pulling out of her embrace. "We'll see. Way too early to be thinking that far ahead. Anyway, I'm going up to my room. I still have some homework I want to finish before dinner."

"Okay…" Though she was dying to know more details, Usagi decided it best after everything that happened to respect their right to privacy. "Oh, oh, wait!"

Thinking of something, she grabbed Shingo's arm and yanked him downwards so that she could whisper in his ear. "By the way, if the time comes that you ever need, you know, _protection_ , I always have some on hand. All you have to do is ask."

Shingo's face turned beet red. "USAGI!"

"What? No glove, no love, Shingo," she lectured with a wag of her finger. "It's important to be safe!"

"Oh, my g—Fine, whatever!" he said, immediately pivoting around and racing up the stairs, two steps at a time.

Mamoru, who had been watching the interactions between Usagi and Shingo in silent amusement, laughed. "What on Earth did you say to him, Usako?"

"Oh, I was just reminding him the importance of safe sex," she said with a shrug of her shoulders. "He's young, but it's not like we waited long…"

"So I remember," Mamoru said, no doubt recalling a certain memorable occasion on the floor of his kitchen.

Her cheeks went flush at the memory as well. "Speaking of which…" Usagi walked back over to the couch, straddling Mamoru's lap. "I don't believe I've received my reward yet."

"Oh?" His hands found their way to her hips, eyes hooded as he stared up at her from behind those sexy reading glasses of his. "Is that so?"

"Uh-huh…"

"Well, we'll have to remedy that, won't we?"

"Uh-huh."

Smiling, Usagi bridged the small gap in between them. She kissed him softly at first, her lips only brushing against his in a gentle tease, but it didn't take long for things to get heated between them. What was meant to be only one kiss turned into many more, all thoughts of studying again leaving their brains as Usagi buried her fingers in Mamoru's hair, moaning when she felt one of his hands move from its spot on her hip to roam up the front of her sweater.

They were so caught up in each other that neither of them heard the front door opening and closing once again, Usagi's mother arriving back home after buying groceries for dinner.

"I'm ho—USAGI TSUKINO, WHAT ARE YOU DOING IN MY LIVING ROOM?"

Yes, graduation _really_ could not come fast enough.

**Author's Note:**

> DISCLAIMER: "Sailor Moon" belong to Naoko Takeuchi.
> 
> AUTHOR'S NOTES: Written for astraearose93 as part of the UsaMamo Spring Exchange 2020. You said you liked manga-verse and Shingo/Hotaru, so I hope you enjoy! 
> 
> Feel free to follow me on Tumblr! My username is kaleidodreams.


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